This invention relates generally to mattress foundation structures and more particularly to a box spring assembly of the type which utilizes non-coil springs. More particularly, this invention relates to a formed wire box spring which is an improvement on applicant's earlier box spring assembly of this type disclosed in U.S. patent application Ser. No. 131,935, filed Mar. 21, 1980 now U.S. Pat. No. 4,339,834. Reference to that application is made for a more detailed description of the background of box spring assemblies utilizing non-coil springs.
The present invention provides a box spring assembly that is an improvement because it utilizes a welded wire grid and supporting springs therefor that are different from the grid and spring assemblies heretofore used and disclosed in the above patent application. The supporting springs of this invention have self-locking tops which are arranged in an "over and under" relationship with a pair of crisscrossed wires in the grid. The springs are self-balancing in the sense that during assembly of the springs with the grid, all of the forces are in opposition to each other. The springs are self-orienting and tend to be self-centering, utilizing leaf spring tension at their upper ends for maintaining an assembly relation with the wire grid. The springs have limited deflection characteristics and, in addition, tend to be very stiff by virtue of their construction so that they normally do not bottom out on the frame. Novel corner springs yieldably support the corners of the welded wire grid on the corners of the supporting frame.